Inspection of defects in friction stir welded Al -7075 alloy using computer tomography

Abstract

The identification of defects is of great interest in the high-quality manufacturing of advance materials. The evaluation of tunnel defects in Al-7075 sheets processed by friction stir welding (FSW) using computed tomography (CT) and finite element method is explored in this work. The effect of axial force and temperature generated during the FSW was assessed. Four rotary speeds were evaluated (1600, 1700,1800 and 1900 rpm), each at two different welding speeds (15 and 30 mm/min). These joints are CT-scanned reconstructing the voxels from the X-Ray images. NEO insights software is used for measurement and evaluation of the voxel data from sectioned zones within the welded joints. It was selected a voxel size of 46 mm, a spot size of 59 mm and a magnification of 4.35 using a Cu filter of 0.5mm. The distance from the x-axis of the X-Ray source was 300 mm. The conditions are observed to differ between each welded joint. The 3D images of the welds showed the forms, places, and levels of the detected defects. The tunnel defects were detected at 2 mm form the bottom edge of the weld plates, and the tendency for the defects were reduce for 1900 rpm based on CT scans. The numerical results of FSW revealed that with higher rotational speed, the heat generated, and strain were increased, while the stress was lowered for higher welding speeds. The coupling of CT and numerical results provide an in-depth understanding of material flow and defect formation during friction process.